Patients are enrolled in clinical trials designed to treat patients with advanced Merkel cell carcinoma (stage 3b or 4). The NIH Clinical Research Center serves as a study site in multi-institutional drug trials. Currently we participate in an open-label phase II study of EMD Serono's anti PD-L1 antibody (avelumab) for the treatment of Merkel cell carcinoma. In addition to the samples collected during the trial for the central protocol, patients seen at the NIH have additional tumor specimens and blood collected to evaluate anti-tumor immune responses during treatment. Trial participants also have the option to enroll in a study on the microbiome in cancer immunotherapy.